The invention relates to a crusher for crushing solid material, the crusher comprising a frame; at least one crusher rotor arranged rotatably to the frame, including crusher blades secured to the circumference thereof and crushing the material; a yielding counterblade structure arranged for co-operation with the crusher blades of the crusher rotor to concurrently crush and cut said material, the counterblade structure being arranged to yield when encountering non-crushable material and when overloaded; and a yielding, downwardly openable set of screens that is arranged below the crusher rotor at a selected axial distance from the crusher blades of the crusher rotor.
On the basis of the running rate the crushers may be divided into two categories: fast and slow running crushers. Fast running crushers are efficient, but they require a feed free from impurities, because, due to a high circumferential speed of the crusher rotor, their structures cannot be protected by automatically released safety means. Additional drawbacks include, inter alia, a fire risk, noise and harmful dust.
Slow running crushers are considerably better suited for crushing various fuel chips, but, due to a slow circumferential speed of the crusher rotor, they are often relatively limited in capacity. Whereas a rise in the circumferential speed implies an increased risk of crusher damage, and this has been tried to prevent by structures whose counterblades give way, when foreign, hard objects or pieces, typically of metal, are caught between the blade and the counterblade.
By using screen meshes surrounding the lower side of the crusher rotor it is possible to better achieve the desired piece size, and it may be possible to avoid construction of a separate screening system that requires large investments.
Known are crusher solutions that include a yielding counterblade, i.e. one that evades a foreign object, or, both a yielding counterblade and a separately openable set of screens. These solutions are complex to implement and they require specific control circuits which have to be controllable in such a manner that they operate synchronously, or one is to confine to manual use only.
Also known are structures where a set of screens and a counterblade are solidly connected, but they are linked to operate on the same side of the crusher rotor, which makes it difficult to remove a foreign object as well as to replace a screen mesh.
Publication US 2011259985 A1 discloses a crusher, in which interconnected counterblade and a set of screens may be collapsed down together to a maintenance position, but neither one of these evades an obstacle jointly or separately.
Publication EP 2113305 A2 describes a crusher, in which a counterblade and a set of screens may both give way separately, but they are mounted on bearings on different sides of the rotor.
Publication DE 102006050051 A1 discloses a crusher, in which counterblades are immovably connected to screen parts, one of which may yield. The counterblades are thus not capable of yielding independently.
In the crusher according to publication U.S. Pat. No. 7,222,805 B1 there are no separate counterblades, but grinding or crushing is performed against a fixed counterpart preceding a set of screens, and against the actual set of screens, which in turn may yield downwardly.
Publication U.S. Pat. No. 5,213,273 A discloses a crusher comprising two assemblies of screens/counterblades (i.e. the screen set is simultaneously a “counterblade”), which yield separately around bearing points locating on different sides of the crusher. Because the set of screens itself serves as a counterblade, there is no independently yielding counterblade.
Publication U.S. Pat. No. 4,917,310 A describes a crusher having a plurality of separate, yielding counterblade configurations (without an actual screens structure) that yield separately about various axes but not as one whole in any circumstances.
Publication EP 0254173 discloses a crusher, in which, below a crusher rotor, there is a structure consisting of two superimposed “screen system sections” where both screen systems may be collapsed together or separately about an axis situating on the opposite side of the rotor with respect to the feeding point of material to be crushed. Said screens structure also forms the actual “counterblade structure” and it does not yield downwardly by itself in any circumstances, because the screens are locked into place with bolts that have to be unlocked before the screens are collapsed down. The presented hydraulic cylinders only assist in moving the screens. The rotation rate of the screens is high and major part of the material to be screened exits through the screens above the rotor.